1. Field of the Invention
This invention relates to oil-based settable spotting fluid compositions for use in cementing wells and subterranean formations and methods of using the compositions.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in the construction of oil and gas wells. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casings and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
A variety of drilling fluids are used in drilling wells. Oil-based drilling fluids are commonly used in applications where the permeabilities of producing formations would be damaged if the formations were contacted by water-based drilling fluids. However, it has heretofore been common place in the industry not to use water-based settable spotting fluids which are incompatible with the oil-based drilling fluids and often cause well bore stability problems and damage to the permeability of producing formations.
During the drilling of a well bore, the drilling fluid used is circulated through the drill pipe and drill bit and then upwardly through the well bore to the surface. The drilling fluid functions to lubricate the drill bit and carry cuttings to the surface where the cuttings and gas are removed from the drilling fluid. While drilling fluids are not settable, i.e., they do not set into hard impermeable sealing masses when static, drilling fluids increase in gel strength over time. Typically, after a well bore is drilled to total depth, the drill pipe and drill bit are withdrawn from the well bore and the drilling fluid is left in the well bore to provide hydrostatic pressure on permeable formations penetrated by the well bore thereby preventing the flow of formation fluids into the well bore.
The next operation in completing the well bore usually involves running a pipe string, e.g., casing, into the well bore. Depending upon the depth of the well bore and whether or not problems are encountered in running the pipe string therein, the drilling fluid may remain relatively static in the well bore for a time period up to 2 weeks. During that time, the stagnate drilling fluid progressively increases in gel strength whereby portions of the drilling fluid in the well bore become increasingly difficult to displace during the cementing process.
After the pipe string has been run in the well bore, the next operation performed is usually primary cementing. That is, the pipe string disposed in the well bore is cemented by pumping a cement composition through the pipe string and into the annulus between the pipe string and the walls of the well bore whereby the drilling fluid in the annulus is displaced therefrom by the cement composition. While a variety of techniques have been developed for improving the displacement of the drilling fluid from the annulus, if the drilling fluid has developed gel strength due to remaining static in the well bore for a long period of time, portions of the drilling fluid in the well bore are bypassed by the cement composition. Since the drilling fluid is not settable, i.e., it does not set into a rigid mass, formation fluids enter and flow in the well bore which is highly undesirable.
Heretofore, settable spotting fluid compositions have been developed and used in wells for various purposes including the early displacement of drilling fluids from well bores. However, as mentioned, the settable spotting fluids have been water based and have included blast furnace slag and other hydraulic components which slowly set at relatively low temperatures. Also, slag-containing settable spotting fluids are intolerant to cement contamination, i.e., if well cement mixes with such spotting fluids, the spotting fluids prematurely set. To prevent a slag-containing spotting fluid from prematurely setting, a very strong set retarder must be added to the spotting fluid and the spotting fluid must be separated from the cement composition by a spacer fluid. If intermixing between the cement composition and the set retarded spotting fluid occurs, the cement composition may be prevented from setting by the strong set retarder in the spotting fluid.
Thus, there are needs for oil-based settable spotting fluid compositions which can be utilized in wells drilled with oil-based drilling fluids and will avoid well cementing problems of the types described above at subterranean temperatures above 90xc2x0 F.
By the present invention, methods of using oil-based settable spotting fluids in well cementing and oil-based settable spotting fluid compositions are provided which meet the above described needs and overcome the deficiencies of the prior art. The methods of cementing a pipe string in a well bore containing oil-base drilling fluids basically comprise the following steps. An oil-based settable spotting fluid is prepared comprising an oil external emulsion which comprises oil, water and an emulsifying surfactant; a hydraulically settable component; and a de-emulsifying surfactant for de-emulsifying the oil-external emulsion when the emulsion is cured. The settable oil-based spotting fluid composition is pumped into the annulus between the pipe string and the walls of the well bore to displace at least a portion of the oil-based drilling fluid out of the annulus. A cement composition is pumped into the annulus whereby the oil-based drilling fluid and the settable spotting fluid are displaced except for portions of the settable spotting fluid which remain in fractures or other permeable zones therein. Thereafter, the cement composition in the annulus and any settable spotting fluid composition remaining in the fractures or other permeable zones therein are allowed to set into hard impermeable masses.
The oil-based settable spotting fluid compositions of this invention for use in cementing wells and subterranean formations basically comprise the following components: an oil external emulsion comprising oil, water and an emulsifying surfactant; a hydraulically settable component; and a de-emulsifying surfactant for de-emulsifying the oil-external emulsion when the emulsion is cured.
The objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
Preferred methods of this invention for cementing well bores or subterranean formations containing oil-base fluids basically comprise the following steps. An oil-based settable spotting fluid is prepared comprising an oil external emulsion which comprises oil, water and an emulsifying surfactant; a hydraulically settable component; and a de-emulsifying surfactant for de-emulsifying the oil-external emulsion when the emulsion is cured. The settable oil-based spotting fluid composition is pumped into the annulus between the pipe string and the walls of the well bore to displace at least a portion of the oil-based drilling fluid out of the annulus. A cement composition is pumped into the annulus whereby the oil-based drilling fluid and the settable spotting fluid are displaced except for portions of the settable spotting fluid which remain in fractures or other permeable zones therein. Thereafter, the cement composition in the annulus and any settable spotting fluid composition remaining in the fractures or other permeable zones therein are allowed to set into hard impermeable masses.
The oil-based settable spotting fluid is prepared by combining a known volume of oil and emulsifying surfactant, or surfactants, which are completely mixed with the oil for uniform dispersion of the surfactant(s) in the oil. An activator, if present, is added to a known volume of water to form a slurry. The water slurry is added to the oil containing the surfactant(s) and the resulting mixture is agitated until a smooth oil-external emulsion is formed. To the emulsion is added the hydraulic material. The emulsion and hydraulic material are completely mixed to form a uniform dispersion of all the ingredients. This is followed by the addition of the required amount of de-emulsifier to the oil-external emulsion. Curing at formation temperature and pressure causes the oil external emulsion to break and release the hydraulic material which sets up as an impermeable mass.
The term xe2x80x9coil external emulsionxe2x80x9d is used herein to refer to the emulsion formed from oil, water and emulsifying surfactant, prior to addition of hydraulic material. The term xe2x80x9coil-based settable spotting fluid composition(s)xe2x80x9d is used herein to mean a fluid which over time will harden into an impermeable mass having sufficient compressive strength to prevent the undesirable inflow or outflow of fluids into the well bore or subterranean formation, but which will not set for a desired relatively long period of time in the range of from about 2 days to about 2 weeks or more. During this time, other operations can be performed, such as placing a pipe string or casing, and conventional cementing operations can be completed.
Suitable oils which can be utilized for preparing the settable spotting fluid compositions of this invention include, but are not limited to, diesel oil, internal olefins, mineral oil and long chain esters. Of these, internal olefins are preferred. The oil used is generally present in the oil external emulsion in an amount in the range of from about 50% to about 90% by volume thereof, more preferably from about 60% to about 80%.
The water utilized in the oil-based settable spotting fluid compositions of this invention can be fresh water or salt water depending upon the particular density of the composition required. The term xe2x80x9csalt waterxe2x80x9d is used herein to mean unsaturated salt water or saturated salt water including brines and seawater. Generally, the water is present in the oil external emulsion in an amount in the range of about 5% to about 45% by weight thereof, more preferably from about 20% to about 40%.
Emulsifying surfactants for emulsifying the oil with water which can be utilized include, but are not limited to, tall oil diethanolamides and a blend of oxidized tall oil fatty acids. A particularly suitable such emulsifying surfactant is a tall oil diethanolamide of the formula RCON(CH2CH2OH)2 wherein R is a C18 to C20 alkyl radical which is commercially available under the trade designation xe2x80x9cAMIDEX(trademark)xe2x80x9d from Chemron Corporation of Paso Robles, Calif. Another particularly suitable such emulsifying surfactant is a blend of oxidized tall oil fatty acids which is commercially available under the trade designation xe2x80x9cOTO MOD #4(trademark)TMxe2x80x9d from Expo Chemical Co. Inc., of Houston, Tex. Tall oil primarily consists of 50% unsaturated fatty acids, chiefly oleic and linoleic acids, and 50% resin acids. Resin acids primarily consist of 90% isomeric abietic acids and 10% is a mixture of dihydroabietic acid and dehydoabietic acids. When used, the tall oil diethanolamide emulsifying surfactant is generally present in the oil external emulsion in an amount in the range of from about 2.3% to about 7.5% by weight thereof. When used, the oxidized tall oil containing oxidized fatty acid blends emulsifying surfactant is generally present in an amount in the range of from about 1% to about 1.6% by weight of the oil in the composition.
Examples of hydraulically settable components that can be used include, but are not limited to, ASTM Class F or the equivalent fly ash together with lime, Portland cement, blast furnace slag, a mixture of silica fume, pozzolan and lime, a mixture of Portland cement and blast furnace slag, and a mixture of Portland cement and pozzolan. Generally, the hydraulically settable component is present in the composition in an amount in the range of from about 100% to about 250% by weight of the oil external emulsion.
ASTM Class F fly ash does not contain lime, and a source of calcium ion is required for it to form a cementitious composition with water. Generally, lime is mixed with ASTM Class F or the equivalent fly ash in an amount in the range of from about 10 to about 30% by weight of the fly ash. Generally the lime and fly ash are present in the composition in an amount in the range of from about 100% to about 200% by weight of the oil external emulsion.
Portland cement is readily available commercially and is made by sintering a source of lime and silica. The Portland cement utilized is generally present in the composition in an amount in the range of from about 100% to about 225% by weight of the oil external emulsion.
Blast furnace slag, as used herein, means a granulated, blast furnace by-product formed in the production of cast iron and broadly comprising the oxidized impurities found in iron ore. The blast furnace slag utilized is generally present in the composition in an amount in the range of from about 100% to about 250% by weight of the oil external emulsion.
Silica fume, also known as condensed silica fume, amorphous silica, silica dust or volatilized silica, is an ultra fine powder by-product material produced in the manufacture of silicon and ferrosilicon. Pozzolan is broadly defined as finely divided siliceous or siliceous and aluminous material that will combine with calcium hydroxide in the presence of water to form a stable compound possessing cementing properties. When a mixture of silica fume, pozzolan and lime is utilized, the mixture generally has a weight ratio of silica fume to pozzolan of about 40:60. Generally lime is added to the mixture in an amount of about 15% by weight of the silica fume and pozzolan. The mixture of silica fume and pozzolan is generally present in the composition in an amount in the range of from about 100% to about 200% by weight of the oil external emulsion.
When a mixture of Portland cement and blast furnace slag is utilized, the mixture generally has a weight ratio of Portland cement to blast furnace slag in the range of from about 80:20 to, more preferably, about 60:40. When utilized, the mixture of Portland cement and blast furnace slag is generally present in the composition in an amount in the range of from about 100% to about 250% by weight of the oil external emulsion.
When a mixture of Portland cement and pozzolan is utilized, the mixture generally has a weight ratio of Portland cement to pozzolan of about 50:50. When utilized, the mixture of Portland cement and pozzolan is generally present in the composition in an amount in the range of from about 100% to about 200% by weight of the oil external emulsion.
Various de-emulsifying surfactants can be used for de-emulsifying the oil-external emulsions when the emulsions are contacted with external water. Such de-emulsifying surfactants include, but are not limited to ethoxylated nonylphenol, quaternized triethanolamine condensate polymer and triethanolamine condensate polymer. A particularly suitable such emulsifying surfactant is an ethoxylated nonylphenol mixture containing 4 moles of ethoxylated nonylphenol and 9 moles of a commercially available ethoxylated nonylphenol which is commercially available under the trade designation xe2x80x9cNP-49(trademark)xe2x80x9d from Union Carbide of Houston, Tex. Another particularly suitable such de-emulsifying surfactant is a quaternized triethanolamine condensate polymer which is commercially available under the trade designation xe2x80x9cCLEARBREAK RT-33(trademark)xe2x80x9d from Chemron Corporation of Paso Robles, Calif. A similarly suitable de-emulsifying surfactant is a triethanolamine condensate polymer commercially available under the trade designation xe2x80x9cCLEARBREAK RT-623(trademark),xe2x80x9d also from Chemron Corporation. When used, the ethoxylated nonylphenol de-emulsifying surfactant is generally present in the oil-based settable spotting fluid of this invention in an amount in the range of from about 0.3% to about 2.5% by weight of the oil external emulsion. When used, the triethanolamine and the quaternized triethanolamine condensate polymer de-emulsifying surfactants are present in an amount in the range of from about 0.3% to about 3.0% by weight of the oil external emulsion.
Although many emulsifying and de-emulsifying surfactants can be used, the surfactants described above are preferred, in part, because they achieve an emulsion with a predictable de-emulsifying time for a variety of base oils and temperatures. They also function well with diesel and kerosene as the base oil as well as other base oils that were previously considered impossible to create settable spotting fluids from.
The resulting oil-based settable spotting fluid is a slurry generally having a density in the range of from about 11 to about 13 pounds per gallon and more preferably from about 11.5 to about 12 pounds per gallon.
In order to prevent foaming when the oil-external emulsion is formed with water, a defoaming agent can optionally be included in the composition of this invention. While various defoaming agents can be used, a preferred defoaming agent comprises polypropylene glycol, particulate hydrophobic silica and a liquid diluent. Such a defoaming agent is commercially available under the trade designation xe2x80x9cD-AIR 3000 L(trademark)xe2x80x9d from Halliburton Energy Services Corporation of Duncan, Okla. When used, the defoaming agent is generally present in an amount in the range of from about 0.01% to about 0.1% by weight of the composition.
In accordance with the methods of the present invention, when a well bore is drilled with an oil-based drilling fluid to total depth and before the drilling fluid in the well bore has had a chance to gain significant gel strength, the drilling fluid is at least partially displaced with the oil-based settable spotting fluid composition of this invention. The oil-based drilling fluid is usually displaced by the oil-based settable spotting fluid composition to a level above those portions of the well bore containing fractures, vugs and other permeable areas or zones. The oil-based spotting fluid composition does not increase in gel strength with time, and it is easily displaced after being static in the well bore for a long period of time, e.g., a time period of two weeks or more. Because the oil-based drilling fluid has not had a chance to increase in gel strength and because the drill pipe includes large diameter drill collars and the like which cause high annular velocity, the displacement of the oil-based drilling fluid is achieved by the oil-based settable spotting fluid composition of this invention.
After the well bore is at least partially filled with the oil-based spotting fluid composition, the pipe string to be cemented is run in the well bore. Depending on how much of the drilling fluid has previously been displaced, and if the pipe string is not floated into the well bore while being filled with the oil-based spotting fluid composition, some drilling fluid will remain in the pipe string. When the well cement composition is pumped through the pipe string into the annulus, the oil-based drilling fluid and the oil-based spotting fluid composition in the pipe string and annulus are displaced ahead of the well cement composition. Because the annulus contains the oil-based spotting fluid composition, any drilling fluid entering the annulus will not have time to increase in gel strength therein and will be readily displaced therefrom by the well cement composition. After the annulus has been filled with cement, the cement in the annulus and any settable spotting fluid composition remaining in the fractures or other permeable zones therein are allowed to set into hard impermeable masses, thereby preventing the entry or flow of formation fluids in the annulus.
In a preferred embodiment of this invention, the hydraulically settable component utilized is one that can be activated by calcium chloride, zinc acetate, zinc formate or mixtures thereof. A preferred such hydraulically settable component is Portland cement. The Portland cement is primarily present in the oil phase of the emulsion while the activator is primarily present in the aqueous phase of the emulsion. When the emulsion breaks, the Portland cement is activated by the water and by the activator, i.e., the reaction is kinetically enhanced by the activator. The activator is generally present in the composition of this embodiment in an amount in the range of from about 2% to about 4% by weight of the hydraulically settable component.
In yet another preferred embodiment of this invention, the hydraulically settable component utilized is one that can be activated by calcium hydroxide, sodium hydroxide, sodium silicate or mixtures thereof. A preferred such hydraulically settable component is blast furnace slag. The blast furnace slag is primarily present in the oil phase of the emulsion while the activator is primarily present in the aqueous phase of the emulsion. When the emulsion breaks, the blast furnace slag is activated by the water and by the activator. The activator is generally present in the composition of this embodiment in an amount in the range of from about 2.5% to about 15% by weight of the hydraulically settable component.
In still another preferred embodiment of this invention, the hydraulically settable component utilized comprises a mixture of silica fume, pozzolan and lime having a weight ratio of silica fume to pozzolan of about 40:60. The mixture of silica fume and pozzolan is primarily present in the oil phase of the emulsion while the lime activator is primarily present in the aqueous phase of the emulsion. When the emulsion breaks, the mixture of silica fume and pozzolan is activated by the lime present in water. The lime activator is generally present in the composition of this embodiment in an amount of about 15% by weight of the silica fume and pozzolan.
In another preferred embodiment of this invention, the hydraulically settable component comprises a mixture of Portland cement and blast furnace slag having a weight ratio of Portland cement to blast furnace slag in the range of from about 80:20 to about 60:40. The mixture of Portland cement and blast furnace slag is primarily in the oil phase of the emulsion. The water phase contains hydrated lime activator in an amount in the range of from about 5% to about 10% by weight of the mixture of Portland cement and blast furnace slag. When the emulsion breaks, lime present in the Portland cement is released by hydration and, in turn, sets up the slag. The hydrated lime activator kinetically enhances the reaction.
In yet another preferred embodiment of this invention, the hydraulically settable component comprises a mixture of Portland cement and pozzolan having a weight ratio of Portland cement to pozzolan of about 50:50. The water phase contains hydrated lime activator in an amount in the range of from about 2.5% to about 5% by weight of the mixture of Portland cement and pozzolan. When the emulsion breaks, the mixture of Portland cement and pozzolan is activated by lime released by hydration of Portland cement. The hydrated lime activator kinetically enhances the reaction.
A preferred method of cementing a pipe string in a well bore containing oil-based drilling fluid comprises the following steps: (a) preparing an oil-based settable spotting fluid composition comprising an oil external emulsion which comprises oil, water and an emulsifying surfactant; a hydraulically settable component; and a de-emulsifying surfactant for de-emulsifying said oil-external emulsion when the emulsion is cured; (b) pumping the oil-based settable spotting fluid composition into the annulus between the pipe string and the walls of the well bore to displace at least a portion of the drilling fluid out of the annulus; (c) pumping the cement composition into the annulus whereby the drilling fluid and the settable spotting fluid are displaced except for portions of the settable spotting fluid which remain in fractures or other permeable zones therein; and (d) allowing the cement composition in the annulus and any settable spotting fluid composition remaining in the fractures or other permeable zones therein to set into hard impermeable masses.
A preferred oil-based settable spotting fluid composition for use in cementing wells and subterranean formations comprises an oil external emulsion which comprises oil, water and an emulsifying surfactant or surfactants; a hydraulically settable component; and a de-emulsifying surfactant for de-emulsifying the oil-external emulsion when the emulsion is cured.
The oil-based settable spotting fluid is prepared by combining a known volume of oil and emulsifying surfactant, or surfactants, which are completely mixed with the oil for uniform dispersion of the surfactant(s) in the oil. The activator, when used, is added to a known volume of water to form a slurry. The water slurry is added to the oil containing the surfactant(s) and the resulting mixture is agitated until a smooth oil-external emulsion is formed. To the emulsion is added the hydraulic material. The emulsion and hydraulic material are completely mixed to form a uniform dispersion of all the ingredients. This is followed by the addition of the required amount of de-emulsifier to the oil-external emulsion. Curing at formation temperature and pressure will cause the oil external emulsion to break and release the hydraulic material which will set up as an impermeable mass.
In order to further illustrate the methods and compositions of the present invention, the following examples are given.